In the course of installing an optical (e.g., laser-based) communication system, the user/installer must adjust the angular orientation of each of a pair of spaced apart optical communication (transmit/receive) units in order to achieve the required line-of-sight alignment therebetween. This adjustment generally requires coordination between two installation personnel, one at each transceiver site, and may typically involve the use of a separate sighting telescope (that has been calibrated at its manufacturing facility) through which the user looks to determine the pointing direction of the optical antenna. While looking through the sighting scope, the user adjusts the orientation of the optical antenna until the remote antenna is centered in the cross-hairs of the sighting scope.
Because calibration of the sighting scope may be carried out in the presence of physical disturbances, and since disturbances may also be present during installation of the optical communication unit, the laser beam transmitted by the optical antenna may not intercept the remote optical antenna, when the unit is adjusted on the basis of the sighting scope alone. The installer may have to-carry out a trial and error visual search routine, with the aid of a person at the remote site, in order to realize accurate beam incidence upon the remote optical antenna. The time required to conduct this exercise adds to the cost of installation.
Moreover, even where the sighting scope is relatively accurately calibrated (either at the factory or by trained personnel at a field site), the initial calibration may impacted over the passage of time due to thermal stresses, vibration and weather. Thus an installed system may be subject to a recurring recalibration cost. In addition to the calibration problem, the user may replace or upgrade one or more subsystems of an installed optical antenna. This may require access to one or more optical antenna components which compromises the line of sight calibration, so that the system has to be recalibrated after the change-out or upgrade.